奥斯特里亚米克

AS1920, AS1922
Triple-Voltage, Micro-Power Microprocessor Supervisory Circuits
D a ta S h e e t
1 General Description
The AS1920 and AS1922 microprocessor supervisory circuits were designed to generate a reset when at least one of the three monitored supply voltages falls below its respective trip threshold.
These very-low-current (6.2µA, typ) devices maintain reset for a minimum timeout period after all supplies have stabilized. Guaranteed to be in the correct state for V CC > +1.0V, these devices are perfect for multiple-volt-age systems with low current requirements and strict monitoring requirements.
The devices are available as the standard products listed in Table 1.
All devices monitor primary and secondary factory-trimmed voltages. Additionally, a third monitoring voltage can be selected via an external resistor divider.
The AS1920 has an active-low push/pull reset output, whereas the AS1922 has an active-low open-drain reset output.
The AS1920 and AS1922 are available in a 5-pin SOT23 package.
Figure 1. Typical Application Diagram
2 Key Features
! Simultaneous Triple-Voltage Monitoring ! Very-Low Supply Current: 6.2µA
! ±1.5% Accuracy Over Temperature
! Reset Time Delay: 200ms
! Power Supply Transient Immunity
! Guaranteed Reset for V CC3 ≥ 1V or V CC18 ≥ 1V
! Active-Low Push/Pull Reset Output (AS1920)
! Active-Low Open-Drain Reset Output (AS1922)
! 5-pin SOT23 Package
3 Applications
The devices are ideal for personal computers, note-books, battery-powered systems, embedded controllers, intelligent instruments, automotive systems, critical CPU monitoring, and any multi-supply monitoring application.
Table 1. Standard Products
Model Output Type Supervisory Voltages AS1920-18Push/Pull 3V, 1.8V, Adjustable AS1922-18
Open-Drain
3V, 1.8V, Adjustable
3V System Logic
1.8V
2.5V
AS1920/AS1922
0.1µF
R 1130k Ω1%R 2100k Ω1%
0.1µF
1RESETN 3V CCA
2GND
4
V CC18
5V CC3
Datasheet - Pi n o ut
4 Pinout
Pin Assignments
Figure 2. Pin Assignments (Top View)
Pin Descriptions
Table 2. Pin Descriptions
Pin Number Pin Name Description
1RESETN Reset Logic Outpu t. This active-low pin serves as the 3V push/pull reset output. A reset is asserted when any one of the supplies are below its respective trip threshold and the reset is held for 200ms after all power supplies have stabilized.
2GND Ground.
3V CCA V CCA. 1V sense, high-impedance input.
Note:If this pin is not used it should be tied to V CC3 or V CC18.
4V CC18V CC18. 1.8V sense input and power detect pin (AS1920-18, AS1922-18). This pin provides power to the output reset stage of the device in order to assert a valid reset when the voltage on the primary input is down.
Note:Bypass this pin to GND with a ≥0.1µF ceramic capacitor.
5V CC3V CC3. 3V sense input and power supply pin (AS1920-18, AS1922-18). This pin provides power to the device.
Note:Bypass this pin to GND with a ≥0.1µF ceramic capacitor.
AS1920/
AS1922
2
GND
3
V CCA
1
RESETN5V CC3
4V CC18
Datasheet - Ab s o l u te M a x i m u m R a t in g s
5 Absolute Maximum Ratings
Stresses beyond those listed in Table 3 may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in Electrical Character-istics on page 4 is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
Table 3. Absolute Maximum Ratings
Parameter Min Max Units Comments V CC18, V CC3, V CCA to GND-0.3V+5V
RESETN Open-Drain-0.3+7V
RESETN to GND-0.3V CC3 +
0.3V
Operating Temperature Range-40+85ºC Guaranteed to meet specified performance from 0 to 70ºC and is designed, characterized and assured to meet the extended temperature limits of -40 to 85ºC but are not tested at these
temperatures.
Storage Temperature Range-65+150ºC
Package Body Temperature+260ºC
The reflow peak soldering temperature (body temperature) specified is in accordance with IPC/JEDEC J-STD-020C “Moisture/Reflow Sensitivity Classification for Non-Hermetic Solid State Surface Mount Devices”.
The lead finish for Pb-free leaded packages is
matte tin (100% Sn).
Datasheet - El e c t ri c a l C ha r a c te r i s ti c s
6 Electrical Characteristics
V CC18 = 1.8V, V CC3 = 3V, V CCA = V CC3, T AMB = -40 to +85ºC (unless otherwise specified). Table 4. Electrical Characteristics
Symbol Parameter Conditions Min Typ Max Unit V RT18Reset Threshold V CC18 1.653 1.683 1.713V V RT3Reset Threshold V CC3 2.763 2.805
2.847V V RTA Reset Threshold V CCA 0.982
1.00 1.018V V CC3, V CC18
Operating Voltage RESETN in Correct Logic State 1
3.3
V I VCC18V CC18 Supply Current V CC18 < V CC3, V CC18 = 1.8V 0.72µA I VCC3V CC3 Supply Current V CC18 < V CC3, V CC3 = 3V
6.2
15µA I VCCA 1
1.Guaranteed by design.
V CCA Input Current V CCA = 1V
-15 0 15 nA I OUT Open-Drain RESETN Output Current Reset Not Asserted, Forced to 0V 24
13µA I LEAK Open-Drain RESETN Output
Leakage Current
Reset Not Asserted, RESETN Forced to 5.5V, T AMB = 25ºC -0.1
0.1
µA
t RST Reset Pulse Width RESETN Low, T AMB = 25ºC 2
2.Measured from the time (t 1) when the input passes through the input threshold voltage (V RT X ) to the time (t 2) when RESETN passes through 1.5V.
140 200 280 ms
t UV
V CC Undervoltage Detect to RESETN
V CC18, V CC3, or V CCA <
Reset Threshold by > 1%
2
T AMB = 25ºC 130
µs
V OL Output Voltage Low, RESETN
I SINK = 2.5mA, V CC3 = 3V,
V CC18 = 0V 0.15 0.4 V
I SINK = 100µA, V CC3 = 1V,
V CC18 = 0V 0.05 0.3
I SINK = 100µA, V CC3 = 0V,
V CC18 = 1V 0.050.3I SINK = 100µA, V CC3 = 1V,
V CC18 = 1V
0.05
0.3
V OH Output Voltage High, RESETN I SOURCE = 1µA (AS1922-xx )
V CC3 - 1V CC3 - 0.65
V
Datasheet - Ty pi c al Op e ra t in g C h a r a c te r i s ti c s
7 Typical Operating Characteristics T AMB = +25ºC (unless otherwise specified).
8 Detailed Description
The AS1920/AS1922 microprocessor supervisory circuits were designed to generate a reset when at least one of the three monitored supply voltages falls below its respective trip threshold.
These very-low-current (6.5µA, typ) devices maintain reset for a minimum timeout period after all supplies have stabi-lized. Guaranteed to be in the correct state for V CC > +1.0V, these devices are perfect for multiple-voltage systems with low current requirements and strict monitoring requirements.Figure 9. AS1920 Block Diagram
Figure 10. V CC Monitor Timing Diagram
AS1920
–+
4
V CC18
5
V CC3
3
V CCA
V CC Internal
–+
Power Detect
–+
Bandgap Reference
1RESETN
200ms Pulse Generator
200ms Delay
V CC3
2GND
1.5V
V CC X
t UV
t RST
RESETN
V RT X
Figure 11. AS1922 Block Diagram
AS1922
–+
4
V CC18
5
V CC3
3
V CCA
V CC Internal
–+
Power Detect
–+
Bandgap Reference
1RESETN
200ms Pulse Generator
200ms Delay
2GND
V CC3
I OUT
9 Application Information
Supply Monitoring
The AS1920/AS1922 are low-power, high-accuracy triple-supply monitoring circuits with a single 200ms microproces-sor reset output.
All V CC inputs (V CC18, V CC3, and V CCA ) must be above their thresholds to prevent a reset from being asserted. The AS1920/AS1922 will assert a reset during powerup, powerdown and brownout conditions on one or all of the V CC inputs.
Power Detect
The AS1920/AS1922 is powered from the 3V input pin (V CC3). The power detect circuitry ensures that the device pulls pin RESETN low as soon as the primary input pin is ≥1V or the secondary input pin is ≥1V.
Powerup
The power detect circuitry ensures that RESETN will be low when either V CC18 or V CC3 ≥1V. As long as any one of the V CC inputs is below its reset threshold, RESETN will stay at a logic low. When all V CC inputs have stabilized, an inter-nal timer will be started and RESETN will be driven high after 200ms.
Powerdown
On powerdown, if any of the V CC inputs drop below its threshold, RESETN is held at a logic low (0.3V) and is guaran-teed until V CC3 and V CC18 < 1V.
Override Functions
As the trip points for V CC3 and V CC18 will always be greater than the trip point for V CCA , if pin V CCA is not used, it should be tied to V CC3 or V CC18. In a similar manner if pin V CC18 is not used it should be tied to V CC3. Tying V CC3 to V CC18 and operating from a 1.8V supply will assure the continuous assertion of RESETN.Note:Pin V CC3 must be used in all configurations.
Ensuring RESETN Valid for Supply Voltages < 1V
When the supplies drops below 1V the RESETN output current sink capability is greatly reduced. Stray currents and stray capacitance to signals other than GND can cause the RESETN output to float. This is not relevant for most appli-cations since most microprocessors and other circuits do not operate with a supply voltage < 1V.
In applications where the RESETN output must be valid down to 0V, a pulldown resistor from pin RESETN to ground will ensure RESETN is held low (see Figure 12).
Figure 12. Typical Application w/Resistor on RESETN Output to GND
The value of the pulldown resistor (R 3) is a trade-off between pulldown strength and loading of the RESETN pin. If the value of R 3 is too large RESETN may still float, and if the value of R 3 is too small it may load RESETN and also use excess supply current, therefore a value of 100k Ω is recommended for the pulldown resistor.
R 3100k Ω
R 2
R 1
3V
1.8V
Adjustable Supply
1RESETN 3
V CCA 2GND
4V CC18
5V CC3
AS1920/AS1922
Figure 13. Triple-Supply Monitor (3V, 1.8V, Adjustable)
Figure 14. Dual-Supply Monitor (3V and 1.8V; Disable V CCA Input)
Figure 15. Dual-Supply Monitor (3V and Adjustable)
AS1920-18
R 2
R 1
3V
1.8V
Adjustable Supply or DC/DC Feed-back Divider
System Reset
To ensure threshold accuracy, set the parallel combination of
R 1 and R 2 ≤ 66.5k Ω
1RESETN
3
V CCA
2GND
4V CC18
5V CC3
AS1920-18
3V
1.8V
System Reset
2GND
1RESETN
3V CCA
4V CC18
5V CC3
AS1920-18
R 2
R 13V
Adjustable Supply or DC/DC Feed-back Divider
System Reset
To ensure threshold accuracy, set the parallel combination of
R 1 and R 2 ≤ 66.5k Ω
1RESETN
2GND
4V CC18
5V CC3
3
V CCA
Figure 16. V CCA Tied to DC/DC Feedback Divider
Figure 17. Triple-Supply Monitor w/Manual Reset Switch
AS1920-18
3V
1.8V
Adjustable Reset Trip Threshold
2.31V
System Reset
2.5V
2.26k Ω1%
27.4k Ω1%
22.6k Ω1%
1RESETN
3V CCA
4V CC18
5V CC3
2GND
AS1920-18
3V
1.8V †
Optional Resistor Recommended to Extend ESD Tolerance
System Reset
2.5V V TRIP = 2.3V
R 1130k Ω0.1%
100nF
100nF
R 2100k Ω0.1%
R 3 †
10k Ω5%
Normally Open Manual Reset
Switch
V TRIP = V CCA /R 2 (R 1 + R 2)R 1 = R 2 ((V TRIP/V CCA ) - 1)
2GND
1RESETN
3V CCA
4
V CC18
5
V CC3
10 Package Drawings and Markings
The devices are available in an 5-pin SOT23 package.
Figure 18. 5-pin SOT23 Package
Notes:
1. All dimensions in millimeters.
2. Foot length measured at intercept point between datum A and lead surface.
3. Package outline exclusive of mold flash and metal burr.
4. Package outline inclusive of solder plating.
5. Complies with EIAJ SC74.
6. PKG ST 0003 Rev A supersedes SOT23-D-2005 Rev C.
Tape and Reel Pin1 Orientation
Datasheet - Or d e ri n g I nf or m a ti o n
11 Ordering Information
The devices are available as the standard products shown in Table 5.
Table 5. Ordering Information
Model Marking Description Reset Type Delivery Form Package
AS1920-18-T ASI1Triple-Voltage Supervisory Circuit:
3V, 1.8V, and Adjustable.
Push/Pull Tape and Reel5-pin SOT23
AS1922-18-T ASI2Triple-Voltage Supervisory Circuit:
3V, 1.8V, and Adjustable.
Open-Drain Tape and Reel5-pin SOT23
Datasheet
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